Introduction to Dermatology 1 Flashcards
The skin arises due to juxtaposition of which two major embryological elements?
Epidermis and the Dermis
What does the epidermis originate from?
The ectoderm
What does the dermis originate from?
The mesoderm which comes into contact with the inner surface of the epidermis
What is the mesoderm essential for enducing?
The differentiation of epidermal structures
What is the epidermis formed as by week 5?
A single basal layer of cuboidal cells
What is the periderm?
A secondary layer of squamous, non-keratinizing cuboidal cells which sits on top of the basal layer of the epidermis
When does the periderm develop?
Week 5
What is the vernix caseosa?
A white waxy protective substance which covers the skin during the last trimester of fetal development
What happens to the basal layer of cuboidal cells from week 11?
The stratus germinativum proliferate to form a multi-layered intermediate zone which consists of four more superficial strata
What are the four superficial strata called?
The Spinosum, granulosum, lucidum and corneum
Where is the stratum lucidum found?
On the palms of hands and the soles of feet
What are dermal papillae?
When the epidermal ridges protrude as troughs into developing dermis beneath neurovascular supply
When does the development of hair follicles occur?
Between weeks 9-13
In which superficial stratum layer do hair follicles develop?
In the stratum germinativum
What is lanugo hair?
soft, feathery hair that can grow all over the body, most often on the back and shoulders.
What cells is the epidermis composed of?
Keratinocytes
How long does the progression from stratum basale to Stratum corneum take?
30-40 days
What is the order of cellular progression of cells in the epidermis?
Starts with basale - then Spinosum, Granulosum, Lucidum and finally Corneum
What process is accelerated in skin conditions like psoriasis?
The cellular progression from the basal layer
What happens to the morphology of the epidermal cells as they progress from basal layer to Stratum Corneum?
They become progressively flatter
What are the special features of the stratum corneum?
They lack nuclei or organelles
What does the filamentous cytoskeleton of keratinocytes consist of?
Actin containing microfilaments
Tubulin-containing microtubules
Intermediate filaments (keratins)
What are the five roles of keratins?
Structural properties
Cell signalling
Stress Response
Apoptosis
Wound Healing
What are desmosomes?
Major adhesion complex in the epidermis which anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocytes
What do desmosomes provide the epidermis with?
Resilience -allow the withstanding of trauma
What are gap junctions?
Clusters of intercellular channels (connexons) which allow connections between cytoplasm of adjacent keratinocytes
What are gap junctions essential for?
Cell synchronization, cell differentiation, cell growth and metabolic coordination
What do adherens junctions engage with?
Actin skeleton
What is the primary role of tight junctions?
They are important in maintaining barrier integrity and cell polarity
what are melanocytes?
They are dendritic cells which distribute melanin pigment to keratinocytes
How does the number of melanocytes change between different ethnicities?
The number of melanocytes does not change, however the amount of pigment they produce does vary
What four other cells are present in the epidermis aside from keratinocytes
Melanocytes, Langerhans cells, Merkel cells and Mast cells
What are Langerhans cells?
Dendritic cells which are antigen presenting and found in the epidermis
What are Merkel Cells?
Mechanosensory receptors
What sits under the epidermis layer?
Basement membrane
What is the basement membrane also known as?
The dermal-epidermal junction
What is the dermal-epidermal junction composed of?
Proteins and glycoproteins including type 4 & 7 collagens, laminin and integrins
What is the role of the basement membrane?
Involved in cell adhesion and cell migration
What layer of the skin is under the basement membrane?
The dermis
How does the dermis arise?
From mesoderm which comes into contact with the inner surface of the epidermis
What are the two layers the dermis is split into?
Papillary dermis and Reticular dermis
What aspect of the dermis layer provides resilience?
The supporting ECM
Which layer of the dermis is closest to the epidermis?
The papillary dermis
Which dermal layer is highly vascular?
Papillary dermis
What is the reticular dermis composed of?
Dense connective tissue
Which dermal layer forms the bulk of the dermis?
The reticular dermis
What is the papillary dermis composed of?
Loose connective tissue
Which proteins are present in the dermis?
Collagen and elastic fibres (fibrillin and elastin)
Which collagen types are present in the dermis?
Type 1 and Type 3
What are the three glycoproteins found in the dermis?
Fibronectins, fibulin and integrins
What do the glycoproteins found in the dermis do?
They facilitate cell adhesion and cell motility